Evaporator temperature-heat flow diagram

Fig. 4 Enthalpy of carbon tetrachloride as a function of temperature at 1 atm A plot of the enthalpy of a system as a function of its temperature provides a concise view of its thermal behavior. The slope of the line is given by Cp. The enthalpy diagram of a pure substance such as water shows that this plot is not uniform, but is interrupted by sharp breaks at which the value of Cp is apparently infinite, meaning that the substance can absorb or lose heat without undergoing any change in temperature at all. This, of course, is exactly what happens when a substance undergoes a phase change you already know that the temperature of the water boiling in a kettle can never exceed 100°C until all the liquid has evaporated, at which point the temperature (of the steam) resumes its increase as more heat flows into the system.

Figure 1 represents the general flow diagram of the multistage flash evaporation process and the solar heat collector system. The process conditions shown are typical for operation with a brine temperature of 140° F., as would be the case during May, June, and August. 

Figure 22.22 shows a flow sheet diagram for a 10 kW HT-PEFC system based on kerosene for a process analysis under realistic conditions verified by experiments. Kerosene was heated in the hquid phase only to 400 K to avoid undesired prereactions. A heat exchanger for air preheating was omitted. Experimental results showed that a certain heat exchange occurs within the metallic construction with no special heat exchanger areas. Water was heated, evaporated, and superheated to 798 K. The mixture of water, air, and fuel led to a mixing temperature of 623 K. 

The same figure also shows the pressure—temperature history of a two-phase test run. This run is represented by the series of points J through P. The points are located as described in the preceding section, with the inlet and outlet of the test section being points L and N, respectively. The interesting feature of this diagram is that somewhere in the test section (between points LandN) the fluid flow became two-phase. This is represented as point M, which is the intersection of the saturation line and the arbitrary extension of line KL. As constructed, point M is arbitrarily located and would probably be better located by the intersection of the saturation line and a vertical line through point , as shown by point iW. The temperature decrease from M (or A/ ) is due to the evaporation of the liquid, where the latent heat of evaporation is used to cool the fluid. 

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